Turkey hasstarted the cross-border bombardment after the threats issued a week ago by Turkish President Tayyip Erdogan to crush Kurdish People’s Protection Units (YPG) militia in Syria's Afrin canton in response to growing Kurdish strength across a wide stretch of north Syria.

Reuters crew filmedTurkish artillery at the border village of Sugedigi firing on Friday morning into Afrin region, and the YPG militia said Turkish forces fired 70 shells at Kurdish villages between midnight and Friday morning. Shelling continued in the late afternoon, said Rojhat Roj, a YPG spokesman in Afrin. Turkish bombardments are the heaviest since Ankara stepped up threats to take military action against the Kurdish region.

Earlier, Turkish media reported that military planning for the offensive was complete and two brigades and 5,000 Free Syrian Army (FSA) fighters were expected to participate. Media reports also stated that General Ismail Metin Temel, a hero of Turkey’s "Euphrates Shield"military incursion into northern Syria in 2016, was handed charge of the Afrin offensive. "Euphrates Shield" was launched on August 24, 2016, and cleared a roughly 2,000 square km area from Islamic State (IS) and YPG control. Officially, the operation was ended in March 2017.

On January 13, the threat was issued after reports that the U.S. plans to create a 30,000-strong Border Security Force (BSF) predominantly made up of Kurdish militias. According to Col. Thomas Veale, the public affairs officer of Operation Inherent Resolve, the U.S.-led coalition is training the Syrian Democratic Forces (SDF) to maintain security along Syria’s borders. SDF is an umbrella group of fighters dominated by the YPG. U.S. State Department spokeswoman Heather Nauert on Thursday urged Turkey not to take any action in northern Syria.

Turkey sees the YPG as an extension of the separatist Kurdistan Workers’ Party (PKK), which is considered a terrorist group by the U.S. and has fought a bloody insurgency since 1984 that has killed at least 35,000 people. With around one-fifth of Turkey’s population identifying as Kurdish, Turkey views the PKK and moves toward Kurdish independence regionally as an existential threat.

On the other hand, the Syrian Kurds have their own fight with Russia-backed Bashar al-Assad's regime where latter is setting its sights on territory held by Kurdish-led forces including eastern oil fields. Till now, SDF has used the power vacuum caused by the civil war to occupy and seize territories in Syria along the Turkish border. But, the question is how much they are open to the concept of greater autonomy within the framework of the borders of the state as proposedby Walid Muallem, Syria's foreign minister in September 2017.

The American Signal

U.S. President Donald Trump decided to arm YPG fighters despite Turkey's objections and a direct appeal from Erdogan at a White House meeting in May 2017. Tensions between the U.S.and Turkey remain high, despite Trump saying last November that Washington would no longer supply weaponsto the YPG. Since then, Ankara has been reinforcing its southern border by sending armored vehicles, tanks, and heavy machine guns, according to local media.

Up until now, the U.S. has been able to deter Russian strikes on SDF forces by launching fighter jet intercepts against Russian jets that cross east and north of the Euphrates river valley. Besides that, there are currently about 2,000 U.S. troops in Syria working with Syrian Kurds. It was unclear how large a contingent of U.S. military might be required for a long-term commitment.

In aspeech at Stanford University's Hoover Institution, the U.S. Secretary of State spelled out a U.S. plan to advance a political transition in Syria to oust Bashar al-Assad. A central pillar of Tillerson’s speech is a UN-supervised election that Tillerson predicted would result in new leadership. Key questions that Tillerson left unaddressed, he continued, included how long Assad should remain in power and whether he would play a role in any political transition.

The Russian Influence

In the current situation, it is Moscow, not Washington, that appears to be dictating the terms of engagement over Syria. Russia has based military observers in Afrin since 2015, and the subject of their removal was part of negotiationsheld between Turkish Army Chief Hulusi Akar and his Russian counterpart Valery Gerasimov and other military and intelligence officials in Moscow on Thursday.

Approximately 180 Russian observers were pulling back from their positions on the Afrin/Turkish border, hours after Turkish artillery began what Ankara said was the "de facto" start of operations against members of the Kurdish YPG militia, which it considers part of the PKK terrorist group. In short, Ankara was waiting for a green light from Moscow.

The Syrian Reaction

“We warn the Turkish leadership that if they initiate combat operations in the Afrin area, that will be considered an act of aggression by the Turkish army,” - Faisal Meqdad, Syria's Deputy Foreign Minister (via State Media Release)

The presence of any Turkish forces on Syrian lands is “totally rejected”, Meqdad added. He said that military action by Ankara would complicate its role as a party to diplomatic efforts and put it on "the same level as the terrorist groups".

With reporting by Al Jazeera, Anadolu Agency, BBC, The Guardian, Reuters and Sputnik International